Semiconductor devices, e.g. appropriate, integrated (analog or digital) computing circuits, semiconductor memory devices such as functional memory devices (PLAs, PALs, etc.) and table memory devices (e.g. ROMs or RAMs, in particular SRAMs and DRAMs), etc. are subject to comprehensive tests in the course of the manufacturing process, e.g. in the semi-finished and/or finished condition, before and/or after being installed in corresponding device modules, etc.
After the installing of a corresponding semiconductor device, e.g. a SRAM or a DRAM (e.g. a DRAM with double data rate (DDR-DRAM=Double Data Rate DRAM), in particular a High-Speed DRAM) in a corresponding device module—in particular after the soldering of the pins of the semiconductor device with the corresponding module pads—it can be tested by means of an appropriate testing apparatus whether the pins of the semiconductor device are safely contacting the corresponding module pads.
In the case of conventional semiconductor devices, the pins are connected internally in the device in general to one or a plurality of protective devices each comprising one or a plurality of diodes (e.g. an ESD structure comprising one or a plurality of diodes each connected e.g. to the supply voltage and/or ground connection).
When relatively high voltages are applied to the pins, the diodes become conductive, and the pins are then connected with the corresponding voltage or ground connection, respectively, in a correspondingly low-resistance manner.
This avoids, during the applying of high voltages, having too high currents flowing in further devices of the semiconductor device connected with the pins (this avoiding a destruction of the further devices).
When, as explained above, it is to be tested whether a particular pin of the semiconductor device is safely contacting the corresponding module pad, current may be imposed upon the corresponding protection diode by the above-mentioned testing apparatus via the corresponding module pad, whereafter the voltage dropping across the diode is measured, or a corresponding voltage may be applied by the testing apparatus at the module pad, whereafter the current flowing through the diode is measured.
When no or only very little current is flowing, it is detected that no or no sufficiently good contacting between the pin and the module pad exists.
Frequently, a plurality of semiconductor devices are installed in one and the same device module (in general such that the semiconductor devices are positioned side by side in one and the same plane).
In order to increase the number of semiconductor devices that can be installed in a device module, in the case of so-called stacked modules the semiconductor devices are—for reasons of space—arranged, contrary thereto, in different planes, in particular such that e.g. every two (or more, e.g. three or four) semiconductor devices are positioned directly one upon the other (with the result that e.g. 18 instead of only 9 semiconductor devices can be installed in a module of particular size).
All (active) pins of the respective top semiconductor device can be connected to respectively corresponding (active) pins of the respective bottom semiconductor device (e.g. by means of corresponding soldering connections)—apart, for instance, from a pin to be triggered separately (e.g. the Chip Select pin or CS pin, respectively) of the top semiconductor device which can be connected to a non-active pin of the bottom semiconductor device (and vice versa)).
After the installing of the corresponding (stacked) semiconductor devices in the corresponding stacked module—in particular after the soldering of the corresponding pins with the corresponding module pads—it can be tested by means of a method corresponding to the method described above whether the pins of the semiconductor devices are safely contacting the corresponding module pads.
This may, for instance, be achieved by a testing apparatus corresponding to the above-mentioned testing apparatus imposing, via the corresponding module pad, and from there via the corresponding pin of the bottom and of the top semiconductor devices, a current upon the corresponding protection diodes which are connected in parallel and are each connected with the corresponding pin of the top or bottom semiconductor devices, whereafter the voltage dropping across the diodes is measured, or a corresponding voltage can be applied by the testing apparatus at the module pad, whereafter the current flowing through the diodes is measured.
When no or only very little current is flowing, a contacting fault is detected.
This conventional testing method has a series of disadvantages.
With the conventional testing method one can, for instance, not—or only with relatively great effort, in particular with a testing apparatus having a very high measuring resolution—detect that e.g. the pin of the bottom semiconductor device is indeed contacting the corresponding module pad sufficiently well, not, however, the corresponding pin of the top semiconductor device (or vice versa) since a relatively high current may flow through the diode connected with the corresponding sufficiently well-contacted pin.
Neither—or only with relatively high effort—can it be detected with the above-mentioned conventional testing method that a soldering connection does indeed exist between the module pad and the pin, but that it is not of sufficiently good quality (i.e. has too high resistance).